1. Field of the Invention
This invention relates to cast articles and in particular to forming composite cast articles having insulating portions intermediate cast portions thereof.
2. Description of the Prior Art
In applications such as exhaust manifold applications, it is desirable to provide an insulative layer so as to reduce the exterior temperature of the manifold such as to 400.degree. F. or less.
One conventional solution to the problem of providing such a low exterior temperature has been to utilize a water cooled manifold. This structure, however, has the disadvantage of increased cost and maintenance as well as in undesirably cooling the exhaust gases, thus preventing possible use of the thermal energy of the gases as with associated apparatus.
In one known form of manifold design, formed and welded sheet metal walls are provided with a formed inner layer of insulation material. In U.S. Pat. No. RE. 28,988 of George E. Scheitlin et al, such an exhaust gas manifold is disclosed wherein the insulating material comprises a layer of compressible material interposed between the inner and outer sheet metal sleeves.
As shown in U.S. Pat. No. 3,173,451 of Games Slayter, a cast manifold with liner may be provided wherein the manifold includes a layer of separate, particulate, highly refractory fibers and a refractory, inorganic binder, with a body of a cast metal bonded to the layer so as to have a portion of the cast metal extend partially into the layer. This structure requires that the binder have a melting point in excess of the melting point of the metal.
Yasuhisa Kaneko et al, in U.S. Pat. No. 3,949,552, show heat insulating castings adapted for use in parts of the exhaust system of an internal combustion engine as well as to other parts through which hot gases, liquid or powders may flow. The Kaneko et al castings comprise triple structure castings including a heat and corrosion resistant metal sheet with a heat insulating refractory material covering a significant portion of the sheet. A cast metal envelope is formed about the sheet and refractory material so as to sandwich the refractory material therebetween.
In U.S. Pat. No. 2,830,343, Harold F. Shroyer discloses a cavityless casting mold and method of making the mold wherein the pattern is provided in a mold body which is burnable by the cast metal as it is poured in so as to be replaced by the cast metal in forming the desired casting. Shroyer teaches the use of expanded plastics, such as polystyrene or polyethylene, as the pattern material.
As shown in U.S. Pat. No. 3,991,808 of John R. Nieman et al, which patent is owned by the assignee hereof, in one form of casting, control of the characteristics of the cast metal is provided by introducing an alloying material into the cast metal as it is poured into the mold. Thus, the alloying, or inoculating, material is maintained at molten form in the casting metal only for a short period of time until the casting metal cools, thereby providing improved reproducible control over the microstructure and final properties of the castings.